It is known to be advantageous to use wood fibers in the composition of a cultivation substrate.
Thus an installation of the above-mentioned type is known from European Patent EP 0 324 689. That document recommends using an installation having two parallel screws turning in the same direction and meshing with each other. Those two screws are provided with threads that are successively forward and reverse threads so as to determine a succession of drive zones and of compression zones, the reverse threads being provided with windows through which the material passes, it being possible for those windows to be smaller for the braking zone of the downstream series than for the braking zone of the upstream series. An adhesive binder for clumping the fibers is fed in during the defibration. The time taken for the material to pass through that installation is very short, and of the order of a few seconds. In order to guarantee that the temperature necessary for sterilizing the fibers is obtained, the machine is provided with heater jackets upstream from the zone at which the adhesive binder is fed in. In addition, insofar as the adhesive binder is a thermosetting binder, the machine is also provided with cooling jackets in the region in which said binder is fed in, so as to prevent it from setting. Thus, that machine is relatively complex and has relatively high energy consumption.
In addition, French Patent FR 2 248 780 filed in 1974, discloses cultivation media made from wood fibers, without addressing in any detail the method of obtaining such fibers.
European Patent EP 0 472 684 discloses a method and an installation for manufacturing a peat-substitute cultivation substrate, and recommends breaking up a fibrous organic material such as wood chips, mixing additional substances with it, and reducing the mixture to fibers and grinding it in a grinder having two contra-rotating parallel screws, with temperature control requiring heating or cooling. The resulting material is not homogeneous and must be sieved so as to recirculate any lumps that are too large into the inlet of the grinder. That document recommends heating the fibers to temperatures lying in the range 60° C. to 120° C. with a view to sterilizing and drying them.